Secondary recovery of petroleum using lpg-aqueous liquid emulsions



July 1l, 1957 c. HARDY ETAL SECONDARY RECOVERY OF PETROLEUM USINGLPG-AQUEOUS LIQUID EMULSIONS Filed Aug. 12. 196s u mun muv INVENTORSWILLIAM C. HARDY 8s BILLY W. MCARTHUR ATTORNE S United States Patent O3,330,348 SECONDARY RECOVERY OF PETROLEUM USING LPG-AQUEOUS LIQUIDEMULSIONS William C. Hardy and Billy W. McArthur, Richardson,

Tex., assignors to Sun Oil Company, Philadelphia, Pa.,

a corporation of New Jersey Filed Aug. 12, 1963, Ser. No. 301,297 1Claim. (Cl. 166-10) This invention relates to the secondary recovery ofpetroleum and has particular reference to improving the drive ofoil-containing fiuid located in heterogeneous formations.

So-called secondary recovery methods involve the drive of theoil-containing fluid (hereafter referred to as the driven fluid andcontaining petroleum oil and/or water and/or gases) from the reservoirrock into producing wells by driving fluids such as water or gas whichare injected into the reservoir through injection wells, both types ofwells being properly located within its extent. Many variations of suchmethods are known, sometimes involving the provision of slugs of variousfluids between the driven fluid and the driving fluid.

The effectiveness of oil recovery by such methods depends upon manyfactors, but one which is quite important is the degree of heterogeneityof' the reservoir rock. The heterogeneity of significance in connectionwith the present invention is that which may be most generally stated asinvolving stratification or lamination of the rock in the direction inwhich flow is desired, with the stratification involving layers varyingquite considerably in permeability. The problem which is presented bythis situation is easily evident: a layer of high permeability willoffer low hydraulic resistance to flow of both the driven and theinjected driving fluid, while a layer of low permeability will offer ahigh resistance to flow. If layers of these various types all containoil, as is usual, the advance of material through the high permeabilitylayers will be much greater than through the low permeability layers,resulting in premature breakthrough and arrival of injected fluid at theproduction wells. Once this occurs, further flow of driving fluid willordinarily take place substantially only through the higher permeabilitylayers, bypassing the low permeability layers which may well have hadtheir oil content displaced only to a relatively small extent.

The condition detrimental to production which has just been outlined hasbeen recognized in the art, and attempts have been made to shut off orplug the high permeability layers at either or both of the injection andproducing wells. It can be readily seen that such a procedure is, atbest, only effective to a quite limited degree. While stratificationusually produces a condition of higher permeability in directionsparallel to the stratification as compared with directions transversethereto, the vast extent of area existing in a usual oil reservoirprovides leakage of flow from low .permeability layers to adjacent highpermeability layers through their interfaces, so that, in effect, whilestreamlines of flow may start out from an injection well along a lowpermeability layer (adjacent high permeability layers being blocked off)they will gradually deviate through boundaries into higher permeabilitylayers and proceed, preferentially, therealong, with the result thatagain the flow which takes place will be largely through the layers ofhigher permeability, with little or no flow through major regions of thelow permeability layers.

In accordance with the present invention the adverse conditions arerectified by the provision in the vicinity of one or more injectionwells of a viscous mobile slug which will form a boundary between thedriven fluid and the driving fluid. As will appear hereafter, this slugwill have greater extent in the direction of flow within the morepermeable layers than in the less permeable layers. The viscosity of theslug offers frictional resistance to flow, to overcome which asubstantial pressure gradient is necessary. The resistance offered is anincreasing function with the extent of the slug in the direction offlow. Once the slug is set up, therefore, a given pressure gradientbetween the injection wells and the production wells will result in amore nearly equal rate of displacement in the layers of differentpermeabilites. Thus a more uniform sweep of all of the permeable layersis produced, resulting in a higher overall removal of the desired oilfrom the reservoir.

The objects of the invention have to do with the effective drive ofpetroleum from layers of different permeabilities, and these will becomemore evident from consideration of the following description of theprocess with reference to the accompanying drawing in which the figureis a highly conventionalized diagram of a vertical section of an oilreservoir taken between injection and production wells.

The reservoir is generally indicated at 2. A plurality of injectionwells are indicated at 4, and a plurality of production wells at 6. Asis usual, multiple wells are thus provided strategically located inaccordance with knowledge of the reservoir dimensions andcharacteristics in order to provide most effective removal of oil.While, as will be evident to those skilled in the art, the reservoir maybe of any one of many types, it may be assumed for simplicity indescribing the invention that a layer 8 of relatively impervious rockoverlies the strata which bear oil. It may also be assumed that theoil-bearing strata are located above another relatively impervious rocklayer 10. Between these boundaries, there are, frequently, fairly welldefined layers which may differ very considerably in permeability in thedirection from the injection wells to the producing wells. These layersmay, of course, slope or have various curvatures, but, commonly, theylie generally parallel to each other, and are conventionalized in theligure as extending generally horizontally. Some of the layers may bediscontinuous; i.e., they may terminate or begin at various locations asviewed in the direction of flow.

Of the layers illustrated, those at 12 and 14 may be considered layersof relatively high permeability in the direction of their extent; layer16 may be considered as of intermediate permeability; and layers 18 and20 may be considered as having relatively low permeability. All of theselayers will generally contain oil, possibly together with water and gas,and the desired results is that of driving their fluid contents from thelocation of the injection wells towards the producing wells. Consideringthe figure to the extent so far described, there may be readilyvisualized what would occur in accordance with conventional practicesutilizing water or gas as the injected fiuid, or utilizing additionallybetween the driving and driven fluids conventional slugs such as thoseof the so-called miscible type. Flow would occur so preferentially inthe layers such as 12 and 14 that rapid displacement would occur thereinas compared with such layers as 18 and 20. Thus these layers 12 and 14of high permeability would be swept out and the driving fluid wouldreach through them the production wells long before even partial sweepthrough the low permeability layers would occur. Once a breakthrough ofthe driving fluid to the producing wells occurred, the effectiveness ofthe recovery process would be severely impaired. The remaining oil inthe low permeability layers would then be recoverable less profitably oreconomically.

In accordance with the present invention, a viscous fluid, of typeshereafter more fully described, is introduced under pressure through theinjection wells 4; or, alternatively, is formed in the formations byintroduction of an injected Huid composition which, as injected,

uid composition giving rise to it is introduced through the injectionwells without the exercise of special control, the uid flowing into thestrata through conventional perforations in the casings of the wells. Asthis lluid enters the various layers, it will obviously meet with lessresistance to flow in the high permeability layers with the result that,as injection proceeds, it will, at any time, radiate substantiallyfurther from the injection wells in the more permeable strata ascompared with the less permeable strata. Ultimately, the injected orproduced viscous fluid will inundate a region around the injection wellsreaching, in the respective layers, the varying boundaries shown at 12',14', 16', 1' and 20'. At the end of this injection, it is generallydesirable to have the slug Volume of the order of 0.5% to of the volumeof oil-bearing fluid which is estimated to be in place in the reservoir.This quantity, however, is subject to extreme variation depending uponthe nature of the formations as determined by coring in the drilling ofthe various wells in the reservoir and from data derived as the resultof primary production. All of the physical characteristics of thereservoir, including dimensions, must be taken into account to ascertainthe proper amount of viscous fluid to be injected or formed. From suchknowledge good estimates of what should be done may be made consideringthe theoretical aspects of what is to occur as will now be described.

Following the injection or formation of the viscous Huid, this willbecome a slug separating the driving uid from the driven uid throughoutthe cross-section of the ow. pattern, and will accordingly be hereafterreferred to as a viscous slug.

The driving fluid is now introduced under pressure and at the desiredrate or rates through the injection wells.

Consider, now, the pressure conditions which will exist. Assume that thepressures at the injection wells are the same, though this, of course,need not be the case since deductions from the known existing conditionsmay indicate that the pressures should differ. Also assume, forsimplicity, that the pressures existing at the producing wells are thesame.

Consider, now, the conditions existing in a high permeability layer suchas 12. As already indicated, the viscous slug will extend to a greaterextent in the direction of ow in this layer as compared with layers oflower permeability, this being the result merely of injection of theslug-forming material. The overall pressure gradient between theinjection wells and the producing wells in this layer 12 will be made upof gradients comprising, first, that across the unswept region of thislayer between the boundary 12' and the producing wells, and, secondly,that between the injection wells and the boundary 12'. The former ofthese gradients will depend upon the velocity (volumetric) ofdisplacement, the extent of its region in the direction of flow, theviscosity of the uid in the unswept region, and the permeability of thelayer 12. In the case of the portion of the slug in this same layer, thegradient between the injection wells and the boundary 12' is similarlydependent upon such matters, the velocity (volumetric) being the sameand the permeability of the layer 12 being the same, but the viscosityof the slug material and the extent in the direction of flow beingdifferent. Since the velocity of ow at any p-oint is a function of thepressure gradient, it will be evident that, as the slug has a greaterextent in the direction of flow, the resulting pressure gradient movingthe in situ fluid will be less so that for a given overall gradient thepro- 4 duction rate through the well 6 from this layer will be less.

Consider next the low permeability layer such as 20. The viscosity ofthe in situ iiuid is here the same as in the layer 12, but thepermeability is less. The viscosity of the slug material in this layeris also the same as that of the same material -in the more permeablelayer. But because of the less horizontal extent of the slug material,the pressure drop tending to move the in situ fluid through the layer 20may be much greater than in the more permeable layer.

Remembering that the initial penetration of the slug material as it wasput in place was dependent upon similar pressure and volumetric velocityaspects, it Will be evident that an automatic adjustment will haveoccurred to the end that, to a fair approximation, when driving liuid isnow injected the volumetric displacement velocities in the variouslayers are more or less equalized, to the end that the slug will travelsubstantially as a unit, more or less maintaining its volumes in therespective layers, and driving the in situ fluid ahead of it toward theproduction wells much as if a rigid piston was operating through all ofthe layers simultaneously. Thus a more uniform sweep of the permeablelayers occurs, with much improved condition of uniformity of removal ofthe desired fluid.

It may also be noted that the situation is to a considerable extentself-adjusting. Suppose, for example, that somehow the slug in the layer20 was initially, or became later, too extended in the direction of flowso as to offer so much resistance that displacement of the uid in thelayer 20 lagged behind that in the layer 12. The slug material in thelatter layer would then advance more rapidly, tending to outdistance theslug in the layer 20. But as soon as this occurred, the leakage betweenlayers would take place, and the viscous slug material would pass intothe layer 12 following the slug material of the latter, so that the`slug material in the layer 20 would be decreased in volume, with theresulting offering by it of less resistance to How, with an accompanyingincrease of rate of displacement in the layer 20. In effect, therefore,the piston provided by the viscous slug is more or less automatically`adjusted in its configuration, always in a sense to tend to maintainequalization of displacement rates in the various layers. This automaticreadjustment will also occur if the layers vary in relative thicknesses.

What has been described is obviously rather conventionalized forsimplicity of consideration. Displacements and displacement rates havebeen treated as if they occurred essentially only along lines betweenthe injection and producing wells. Obviously, the flow conditions aretwo-dimensional in the layers and the boundaries are not well-defined,though definition is usually reasonably sharp. But it will be evident,without further elaboration, that what has been described is moregenerally true for this two-dimensional type of flow. The boundariesbetween the slug and the driven fluid, and between the slug and thedriving fluid, though curved, and varying with the progress of thedrive, will, generally, conform to the desired conditions in which theslug as a whole, varying in its shape, will act essentially as a pistonto drive the driven fluid uniformly through the Various layers. Asviewed from above the slug would appear as an annulus having ratherirregular boundaries expanding outwardly with the drive and bulgingtowards the production wells, i.e. in the direction of freer flow. Withits outward expansion its width. would decrease, maintaining, however,substantial equalization of flows in the various layers by the actionsalready described.

In the foregoing discussion it was pointed out that generally thevarying permeabilities of the layers would result in the introduction ofslug material (i.e., the ultimate viscous material of the slug or thematerial giving rise to the viscous slug) variably thereto in conformitywith what is desired, even though no control of introduction of the slugmaterial at various levels was elfected. However, where observedconditions would seem to warrant, the slug material may bedifferentially injected into various layers by the use of packers infashions well known in this art for injection of fluids where desired.By the use of packers, injection of the slug material may be cut oftfrom the less permeable layers for selective major introduction into themore permeable layers, and proportioning of the amount of slug materialintroduced into the layers may be thus controlled. The initialvolumetric shape of the slug may thereby be made whatever seemsdesirable to the operator. In a highly permeable layer, for example, itmay be desirable to introduce a much greater amount of the slug materialthan would proportionately 1go thereinto merely by uncontrolledinjection into all of the layers.

The nature of the viscous slug material provided in accordance with thisinvention may vary considerably but is characterized by its formation asan emulsied slug. The emulsiiied slug is a preformed emulsion of twoliquids.

The emulsion is desirably introduced in a volumetric amount estimated tobe 0.5% to of the oil in place in the reservoir. The introduction may beeither controlled selectively to the various strata by packers or theintroduction may be uncontrolled, as brought out above, to permit theportions entering the various layers of s-trata to do so in amountsautomatically controlled by the permeability of the layers.

The liquid emulsion thus provided may be either of oil-in-Water type orwater-in-oil type, either being effective.

In the case of either type of emulsion, the emulsion may be provided inany of the well-known conventional fashions and these need not bedetailed. For example, homogenization may be effected by high velocityflow of a mixture of the liquids and an emulsifying agent under highpressures through restricted passages; or the emulsilication may beeffected by the use of supersonic vibrations or by mechanical vibrationscreating intense turbulence in any desired fashion.

While not essential, increase of effective viscosity of the slugmaterial may be achieved by increasing the viscosity of the liquidforming the continuous phase. In the case of a `water-in-oil emulsion,the oil may be of naturally high viscosity type, or a less viscous oilmay have its viscosity increased by the addition of such materials asolelin polymers, soaps, still bottoms, or high viscosity crude oil.

In the case of oil-in-water emulsions, the aqueous phase may have itsviscosity increased by the incorporation of carboxy methyl cellulose orother gel-forming or viscosity-producing materials such as sodium laurylbetaaminopropionate, hydrolyzed polyacrylamide having 12 to 45 percentof the original carboxamide groups hydrolyzed to carboxyl groups,polysaccharide gums, agar, d-galactopyranose residues attached by 1,3glycosidic linkages, algin-polyurenic acid, orcarrageenin-polysaccharides of d-galacto pyranose and l-galactose units,Z-ketogluconic acid units and nonreducing sugar units, each unit thesize of a hexose and combined with one sulfate radical.

In the case of either type of emulsion, suitable emulsifying agents maybe used corresponding to the type of emulsion desired. Conditions foremulsification of the two types are well known and need not beelaborated here. For example, organic acid-additive salts of N-higheralkyl substituted alkylenepolyamines may be used for the formation ofoil-in-water emulsions. Numerous other wellknown emulsifying agents maybe used. In the case of oil-in-water emulsions typical emulsifyingagents may be polyoxyethylene sorbitolA monostearate, polyoxyethylenesorbitol monopalmitate, polyoxyethylene sorbitol monooleate,polyoxyethylene stearate, polyoxyethylene oxypropylene stearate,polyoxyethylene lauryl alcohol, polyoxyethylene cetyl alcohol,polyoxyethylene stearyl alcohol, polyoxyethylene oleyl alcohol, acidstable glyceryl monostearate, or alkyl aryl sulfonate.

The emulsifying agents used to produce water-in-oil emulsions may be,for example, sorbitan sesquioleate, sorbitan monooleate, sorbitantrioleate, sorbitan monostearate, sorbitan tristearate, sorbitanmonopalmitate, sorbitan monolaurate, glyceryl monostearate, or glycerylmonooleate.

As the continuous phase of a waterinoil emulsion, there may be usedliquefied petroleum gas containing a viscosity-increasing material, andthe advantages of the invention already described may be achieved withthe additional advantage of providing a miscible slug with its knownresult of effecting a more complete removal of the desired petroleumcontent under gas drive. Whatever the type of slug used, the drive maybe either by gas or by water, but gas drive is desirable when a miscibleslug is used.

It will be evident that a combined water and gas drive may be used. Inthe case of a miscible slug gas may be first introduced as the drivingmaterial, followed by water.

The effective viscosity of the slug of emulsion is, in accordance withthe invention, not so much due to the actual viscosity of the continuousphase as to the socalled Jamin effect. The Jamin eifect is due to theresistance to flow produced by the material forming the discontinuousphase which, in a sense, blocks the pores of the formation so that theslug material, viewed as a whole, has an apparent high viscosityexceeding that of the fluids in the reservoir. As already stated, theviscosity may be further increased by actual increase of viscosity ofthe continuous phase. The apparent viscosity is desirably at leasttwenty percent greater than that of I the oil in the formation.

Emulsions are advantageous in that they exhibit the properties of adilatent material, i.e. one which has the characteristic of exhibitingan increase in viscosity during intense agitation. A more accuratestatement would be that the shear forces increase with shear rate, thebehavior being different from that of a thixotropic material whichexhibits an increase in shear forces with a decrease in shear rate.

The high velocity channels will thus create a higher hydraulicresistance in the case of emulsions, as is desirable in the case of amobile slug of the type herein considered. If flow in a channel ceasedcompletely or became quite slow, the emulsion would have a tendency tobreak re- Irucing the hydrualic resistance and thereby reestablishingThus, a wide range of viscosities may be made available for use inaccordance with the results desired. What should be used will generallybe determined by preliminary tests of liow conditions using samples ofporous materials corresponding to those secured by coring of theformations. As is well known, deductions as to flow conditions may bemade by taking into consideration previous history of the particularreservoir being operated. The deductions are made from pressure and flowmeasurements, composition of produced fluids, etc. The engineers incharge of operations may thus make their best estimates as to thedesired properties of a slug to be used for driving purposes.

It will be evident that numerous variations in procedure may be adopteddepending upon conditions observed, and the invention is accordingly notto be considered as limited except as required by the following claim.

What is claimed is:

The secondary recovery method for petroleum-containing fluid from areservoir containing said fluid in layered formations of varyingpermeabilities which includes:

introducing through at least one injection well into said reservoirmaterials to produce in the reservoir a slug having the form of anemulsion with a liquid continuous phase of liquefied petroleum gas andan aqueous discontinuous phase, the slug having a higher eiectiveviscosity than the petroleum-containing uid in the reservoir and varyingin penetration with said formations; and

then providing a fluid drive through said injection Well to advance saidslug to drive before it the petroleumcontaining fluid towards at leastone producing well.

References Cited UNITED STATES PATENTS 2,771,138 11/1956 Beeson 166-92,827,964 3/1958- Sandiford etal. 166-9 8 Maly 166-9 Habermann 166-9 XBinder et al. 166-9 Meadors et al. 166-9 Binder et al. 166-9 OTHERREFERENCES- Becher: Emulsions: Theory and Practices, Reinhold PublishingCorp., N.Y. (1957), pages 338, 339. 341-346. lo 3504354, 356 and358-360.

CHARLES E. OCONNELL, Primary Examiner.

S. J. NOVOSAD, Assistant Examiner.

